Number 675, March 3, 2004
by Phil Schewe and Ben Stein
The Accelerating Expansion
The accelerating expansion of the universe, the notion that the big
bang enlargement of spacetime is not slowing down but actually gathering
speed, has received new experimental support in the form of supernova
observations made by the Hubble Space Telescope (HST).
Previous evidence for such a cosmic acceleration consisted of studies
of the dimness of remote supernovas (Update
355), and represented a major revision for some scientists who had
long thought that the mutual gravity among galaxies would slow or even
reverse the cosmological expansion. The new HST observations consist
of reexaminations of 170 previously studied supernovas and the announcement
of 16 new objects, including 6 of the 7 most distant type Ia supernovas
yet recorded.
The new data are in line with the accelerating-expansion hypothesis
employing the mysterious mechanism usually referred to as "dark energy."
The energy of the universe would be divided up as follows: 29% in the
form of matter (dark plus luminous) and 71% as dark energy. (NASA press
conference, 20 Feb; Riess et al., preprint astro-ph/0402512
)
Sub-Wavelength Lensing
Sub-wavelength lensing in flat panels of left-hand materials (LHM)
has been seen in two new experiments. What this means is that a planar
sheet---and not something that has to be machined into a traditional
lens shape---can be used to focus light into a tight spot. The size
of this spot, furthermore, is less than half the wavelength of the light
being used.
Getting around the venerable "diffraction limit" (whereby an object
smaller than the wavelength is difficult to image) would be a boon to
optics (in the microwave range, for example, wireless communications
would benefit at the level of cell phones and base stations) and is
normally achieved only by parking the object very close to the source
of the illumination.
Left-handed materials (so called because the "right-hand rule" used
by physicists to picture the relation between a light pulse's electric
and magnetic fields and its line of propagation is here reversed) possess
a negative index of refraction. This fact, in turn, means that a light
ray approaching from air into the LHM material will be deflected not
toward but back and away from a line drawn perpendicular to the surface
of the material. It is this bizarre deflection that leads to novel optical
effects.
When the idea of the LHM phenomenon was first propounded, many felt
that such materials could not exist. Even after the first experiments
were reported (Update
476) skepticism lingered. Later more evidence arrived showing preliminary
lensing effects with flat panels, the hallmark of LHM optical abilities
(Update
628).
Now, two groups have more direct evidence for flat-panel lensing and
for better-than-wavelength focusing. George Eleftheriades and his colleagues
at the University of Toronto (gelefth@waves.toronto.edu; 416-946-3564;
see his
website), using a material devised from printed metallic strips
mounted on a plane and sandwiched between two patterned sheets, show
that a source of microwaves can be lensed better than the diffraction-limit
would allow, but not into a "perfect focus" called for in some LHM theories.On
the positive side, the energy losses in the material which some commentators
had predicted would hamper prospective LHM lenses (and their potential
use in medical imaging or radar sets, say), were actually quite minimal.
Meanwhile, Vladimir Kissel and his associates at the Institute for
Theoretical and Applied Electromagnetics in Moscow (kis_v@mail.ru, +7(095)4842644)
have also observed "superresolution" in their lensing of microwaves
with a flat panel, achieving a spatial resolution as good as one-tenth
the wavelength. (Toronto group, Grbic and Eleftheriades, Physical Review
Letters, upcoming article; Moscow group, Lagarkov
and Kissel, Physical Review Letters, 20 February 2004)
Bubble Fusion
Bubble fusion, the apparent generation of fusion energy through the
violent collapse of bubbles in a liquid tank, has been reported in a
paper about to be published in Physical Review E (Taleyarkhan et
al., upcoming, probably March 2004). The paper, a followup to a
controversial report published two years ago (Update
579), describes "statistically significant neutron and gamma ray
emissions" after sound waves and pulsed neutrons hit a chilled liquid
acetone tank spiked with deuterium fuel.
The researchers (Rusi Taleyarkhan, formerly at Oak Ridge but now at
Purdue, 765-494-0198, rusi@purdue.edu) report the observation of flashes
of light (sonoluminescence) as well as the emission of neutrons with
energies of less than or equal to 2.5 MeV---what you would expect if
pairs of deuterium nuclei were fusing together to produce energy in
their setup.
While the researchers describe various improvements to their experimental
setup, in response to comments received on their original paper 2 years
ago, critics (including Aaron Galonsky, Michigan State, galonsky@nscl.msu.edu)
still have a number of concerns. According to Galonsky, the authors
have not demonstrated that the sonofusion data for neutron emission
is free of gamma-rays. While separating neutron and gamma-ray signals
is challenging, it is necessary to have a clean neutron-only spectrum
to have an unambiguous demonstration of nuclear fusion.
Willy Moss of Livermore (925-422-7302, wmoss@llnl.gov) says "Although
I believe that thermonuclear sonofusion [not to be confused with cold
fusion] may not be impossible...I am still not convinced... I believe
that additional tests need to be done and many should have been performed
and discussed in the paper, for example...if neutrons are being generated,
then how about moving the scintillator further away from the sample
to see if the signal decreases, due to the decreasing solid angle of
the detector?"
(Other experts, Richard Lahey, RPI, laheyr@rpi.edu, 518-276-6614, a
co-author on the paper; Mike Saltmarsh, Oak Ridge, 865-576-6915, saltmars@mail.phy.ornl.gov,
co-author of a paper that attempted to duplicate the initial results
but reported a null result---see Shapira
and Saltmarsh, Phys Rev Lett, 19 August 2002)
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